To counter the specific situation you have described there are two possibilities: to escape alive, or to kill him outright. In my opinion, trying to go one-on-one with Huskar is almost always ill-advised due to his skill set. So I have broken this up with heroes that can reasonably escape while still damaging Huskar to a degree and lastly a hard counter.
Windrunner - using the
windrunner ability, depending on level, you have from 3-5 seconds of 100% evasion, 50% increased move speed, and a small area of effect slow around your hero. While this skill can usually be advised for aggressive engagement usage, as an escape, it is ideal to run from Huskar.
Shackleshot is also a solid escape tool depending on your ability to position yourself and predict the enemy's movement.
Mirana - even while being attacked, with a few steps back
starfall should be relatively easy to land for either a small stun (if early levels) or a large amount of nuke damage (later levels). Huskar's skills are all based around losing health and gaining bonus damage so burst damage is your friend here. In an ideal situation you would have teammates that could follow-up with finishing the kill, but most likely you can turn at this point and
leap toward safety.
Leap is also a pretty solid counter to Huskar's ultimate,
Life Break. Where
Life Break was suppose to slow for 5 seconds, after
leap you will gain some move speed back due to the leap move speed bonus.
Anti-Mage - dive in to add a few attack swipes before using blink to escape in any direction, blinking in a direction other than straight back will help as it is less expected.
Void - similar tactic to Anti-Mage, but using
Timewalk instead and with the added perk of
Chronosphere to either give you more time to attack or get away.
[Hard Counter] Spectre - With
desoloate adding damage since you are one on one, and
dispersion soaking up anywhere between 10-22% of damage dealt to you, the only large variable here is whether your items are farmed yet.
Force staff - push yourself in some direction away from attack.
Eul's Scepter - use on Huskar if you are alone and need to run or on yourself to allow teammates to focus down Huskar and you can rejoin a few seconds later either to use nukes that were on cd or hopefully persue a now heavily injured Huskar.
Sheep-stick - polymorph/hex as a counter for any carry, for the most part.
Ghost Scepter - you can still be attacked through manually casting of Huskar's orb, but this will be far far slower than if he was auto-attacking with his
berserker blood buff.